Electrolytes and the liver and kidneys: is it safe

Electrolyte drinks, tablets, and powders have long become a familiar part of endurance training. But it is the kidneys that are responsible for the balance of sodium, potassium, and magnesium, so a logical question arises — do such supplements harm the kidneys and liver. The editorial team explains in which cases electrolytes are safe and in which they can become a problem.

The kidneys as the main regulator of electrolytes

Electrolytes are minerals that carry an electrical charge in solution: sodium, potassium, chloride, magnesium, calcium, bicarbonate. Blood volume, the work of nerves and muscles, and heart rhythm depend on their concentration. The body keeps them within very narrow limits, and the main work here is done by the kidneys.

Every day an enormous amount of sodium is filtered through the glomeruli of the kidneys, and over 99% of it is reabsorbed back in the tubules. The precise «tuning» takes place under the control of hormones: aldosterone, antidiuretic hormone, natriuretic peptides. When a person eats more salt, the kidneys simply excrete more.

The same applies to potassium: healthy kidneys are able to quickly increase its excretion in response to intake. That is why, in a person with normal kidney function, electrolyte supplements at reasonable doses rarely cause dangerous changes in blood levels.

The situation changes when the kidneys work worse. With a decrease in GFR, the ability to excrete potassium, magnesium, and phosphates decreases, and what for a healthy person is an ordinary serving may become an excess for a patient with chronic kidney disease.

The liver plays a smaller role in electrolyte metabolism, but in cirrhosis the balance of sodium and water is disturbed: edema and ascites develop, and doctors restrict salt. So for the liver the question of electrolyte safety is relevant primarily in the presence of severe disease.

Sodium: benefit for the athlete and its limits

During prolonged training a person loses sodium in sweat, and its concentration in sweat is highly individual. The ACSM position statement on fluid and exercise (Sawka et al., 2007) indicates that adding sodium to a drink during prolonged exertion helps retain fluid and reduces the risk of hyponatremia.

For healthy kidneys a single intake of sodium from an electrolyte drink is not a problem. The risk rises when a person takes salt tablets «just in case» on days without exertion, and their total salt intake already exceeds WHO recommendations (less than 2 g of sodium per day for the general population).

Chronic sodium excess is associated with elevated blood pressure, and hypertension is one of the main causes of kidney damage. That is, the danger is not in the drink itself, but in the fact that regular «extra» salt adds a load on top of an already high background.

For people with arterial hypertension, heart failure, liver cirrhosis, or CKD, a doctor often restricts sodium. For them, mindless use of salt capsules can cause fluid retention and worsening of the condition.

At the same time, too low a sodium intake on long races is also dangerous — because of hyponatremia, to which a separate section below is devoted.

Potassium and magnesium: when the kidneys cannot keep up

Potassium is the most «sensitive» electrolyte from a safety standpoint. Both a deficiency and an excess of potassium (hyperkalemia) can disturb heart rhythm. In a healthy person, potassium from food and moderate supplements is quickly excreted, but in CKD, and also against the background of certain medications, this mechanism weakens.

Medications that retain potassium include ACE inhibitors, angiotensin receptor blockers, potassium-sparing diuretics (spironolactone), and also some NSAIDs. A person who takes such medications and at the same time drinks electrolyte beverages containing potassium or uses potassium salt substitutes risks developing hyperkalemia.

Magnesium has a wide margin of safety for healthy kidneys: an excess from supplements usually manifests as diarrhea rather than toxicity. However, in patients with severe kidney failure magnesium accumulates, and hypermagnesemia can cause weakness, a drop in blood pressure, and disturbances of cardiac conduction.

That is why the instructions for many magnesium and potassium preparations carry a warning about kidney failure. For sports electrolyte mixes the doses are usually moderate, but when several products are combined the total intake can be noticeable.

Hyponatremia: a risk not from supplements but from water

The paradox of endurance sport is that the most dangerous electrolyte condition is associated not with an excess of minerals but with an excess of water. Exercise-associated hyponatremia occurs when a person drinks more than they lose in sweat and urine, and the sodium in the blood becomes «diluted».

The consensus on exercise-associated hyponatremia (Hew-Butler et al., 2015) emphasizes that the main cause is excessive fluid intake, and sodium in drinks only partly reduces the risk. Severe hyponatremia is accompanied by cerebral edema and can be fatal.

In this context the kidneys are a «victim» of the situation: during prolonged exertion the release of antidiuretic hormone reduces the kidneys' ability to quickly excrete excess water. So even healthy kidneys cannot always compensate for excessive drinking.

The practical conclusions of the consensus are simple: drink according to thirst, do not gain weight during a race, and use electrolyte drinks as a supplement rather than as a way to «safely» drink without limits.

• nausea, headache, disorientation during or after a long race;
• swelling of the fingers, weight gain after the run;
• confusion, seizures — an emergency condition.

How to use electrolytes safely

For a healthy person, electrolyte supplements make sense primarily during prolonged (over 60–90 minutes) or very hot training, and also with heavy sweating. On an ordinary day without exertion, the diet usually provides a sufficient amount of minerals.

Before regular use it is worth paying attention to the composition: how much sodium, potassium, and magnesium a serving contains and whether these minerals are duplicated in your other supplements. The total dose from several products often turns out to be higher than it seems.

People with diseases of the kidneys, liver, or heart, and also those who take blood pressure medications or diuretics, should coordinate electrolyte supplements with a doctor. Basic monitoring is potassium, sodium, creatinine with a GFR calculation, and if needed magnesium.

Interruptions in the heart's work, muscle weakness, pronounced edema, or a sharp decrease in the amount of urine should raise concern. Such symptoms require medical evaluation, not an increase in the electrolyte dose.

Editorial conclusions

For healthy kidneys, electrolyte supplements in reasonable amounts are safe: the kidneys easily excrete an excess of sodium, potassium, and magnesium. For the liver they are neutral, provided there is no severe disease disrupting the water-salt balance.

The real risks concern three scenarios: chronic kidney disease, taking medications that retain potassium, and excessive drinking during long races that leads to hyponatremia. In these cases, what matters is not the «right brand» of electrolytes but medical monitoring and a sensible hydration strategy.

The best practice is to use electrolytes as directed, during real exertion, and to count them as part of the total mineral intake.

For a deeper understanding of the topic we recommend our materials on hydration during a marathon, on magnesium for athletes, and on creatine and the kidneys.

References

1. Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390.
2. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med. 2015;25(4):303–320.
3. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine joint position statement. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543–568.
4. Palmer BF, Clegg DJ. Physiology and pathophysiology of potassium homeostasis. Adv Physiol Educ. 2016;40(4):480–490.
5. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int Suppl. 2013;3(1):1–150.
6. World Health Organization. Guideline: sodium intake for adults and children. Geneva: WHO; 2012.
7. World Health Organization. Guideline: potassium intake for adults and children. Geneva: WHO; 2012.